With recent advance in the technology of microfabrication on a substrate, much attention is now focused on the micromachine technologies to form on a substrate (such as silicon substrate and glass substrate) microstructures and their control components (such as electrodes and semiconductor integrated circuits).
One of such technologies is disclosed in Non-Patent Document 1. (C. T.-C. Nguyen, “Micromechanical Components for Miniaturized Low-power Communications” (Invited Plenary Proceedings), 1999 IEEE MTT-S International Microwave Symposium RF MEMS Workshop, Jun., 18, 1999, pp. 48–77.)
The author of this literature proposes using a microresonator as a high-frequency filter for wireless communications. FIG. 14 shows such a microresonator 100, which is comprised of a substrate 101, an output electrode 102a, and a resonator electrode 103, with a space A interposed. The resonator electrode 103 has its one end connected to the input electrode 102b which is made of the same conductive layer as the output electrode 102a. When a voltage with a specific frequency is applied to the input electrode 102b, the beam (vibrating part) 103a of the resonator electrode 103 (which is placed above the output electrode 102a, with a space A interposed) vibrates at a natural frequency. This vibration changes the capacity of the capacitor constructed of the space A between the output electrode 102a and the beam (vibrating part) 103a. This change is output through the output electrode 102a. The high-frequency filter relying on the microresonator 100 mentioned above realizes a higher Q-value than those relying on SAW (surface acoustic wave) or FBAR (film bulk acoustic resonator).
The microresonator mentioned above is produced in the following manner. First, referring to FIG. 15A, a substrate 101 coated with an insulating film is prepared. On this substrate 101 are formed from polysilicon an output electrode 102a, an input electrode 102b, and a supporting electrode 102c. The first one 102a is held between the second and third ones 102b and 102c. The substrate 101 and the electrodes 102a to 102c are entirely covered with a sacrificial layer 105 of silicon oxide.
Second, referring to FIG. 15B, contact holes 105b and 105c reaching the input electrode 102b and the supporting electrode 102c are made in the sacrificial layer 105. Then, a polysilicon layer 106 is formed on the sacrificial layer 105 and in the contact holes 105b and 105c. 
Third, referring to FIG. 15C, the polysilicon layer 106 undergoes pattern etching, so that a beltlike resonator electrode 103 passing above the output electrode 102a is formed. Pattern etching is performed in such a way that the contact holes 105b and 105c are kept covered completely for protection of the input electrode 102b and the supporting electrode 102c from etching.
Finally, the sacrificial layer 105 is selectively removed to form a space A between the output electrode 102a and the resonator electrode 103. Thus, there is obtained the microresonator 100 as shown in FIG. 14.
The microresonator 100 constructed as mentioned above has a natural frequency which depends on its beam length L (the length of the beam 103a) as shown in FIG. 16. It is noted from FIG. 16 that the theoretical natural frequency according to the equation (1) below is proportional to 1/L2. This implies that it is necessary to reduce the beam length L in order to achieve a high natural frequency.
                              f          R                =                                            0.162              ⁢                                                          ⁢              h                                      L              2                                ⁢                                                    E                ⁢                                                                  ⁢                K                            ρ                                                          (        1        )            where, h: film thickness
E: Young's modulus
K: magnetic coupling ratio
ρ: film density
The disadvantage of the above-mentioned microresonator 100 is that the beam length L cannot be made smaller than the width of the output electrode 102a because the space A and the resonator electrode 103 are formed over the output electrode 102a. 
If the beam length L is to be reduced to increase the natural frequency, it is necessary to reduce the width of the output electrode 102a. This results in a decrease in capacity between the output electrode 102a and the resonator electrode 103, which in turn decreases output. This is the reason why it is impossible to increase the natural frequency by reducing the beam length L.
It is an object of the present invention to provide a micromachine and a method for production thereof, the micromachine having a resonator electrode that makes it possible to increase the natural frequency by reducing the beam length.